Manufacture of wood-screws.



No. 877,157. PATENTED JAN. 21, 1908.

' W. G. ALLEN.

MANUFACTURE OF WOOD SCREWS.

APPLICATION FILED .TAN.30, 1906.

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No. 877,157. 'PATENTED JAN. 21, 1908.

w. G. ALLEN. MANUPAOTUREOF WOOD smmws;

APPLICATION FILED JAN. 30, 1906.

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1 UNITED STATES PATENT caries,

WILLIAM G. ALLEN, OF HARTFORD, CONNECTICUT, ASSIGNOR TO THE GLOBE SCREW COMPANY, OF HARTFORD, CONNECTICUT, A CORPORATION OF CONNECTICUT.

MANUFACTURE or woon scnaws.

Specification of Letters Patent.

Patented Jan. 21, 1908.

Application filed January 30- 1906. Serial No. 298.730.

To'all whom it mag concern: I I I Be it known that I, WILLIAM GALLEN, of

Hartford, Connecticut, have invented a new;

and useful Improvement in the Manufacture of Wood-Screws, which invention is'fully set cuts ofl'a Iportion of the metal of the blank from whic l the screw is formed. Extended elforts'have heretofore been made to produce wood-screws having the desirable and for mbst uses requisite characteristics of cutscrews, at the same time avoiding the expense of the cutting. To that end various-ways of forming the'screw-threads by the'action of relatively movable dies have been proposed the resulting screws being commonly referred. to as rolled screws. But so far as I am aware the onl y"rolled screws that have been marketed and used to any material extent have objectionable characteristics (some of which are mentioned hereafter) which render them inferior to, and hence unable to compete with, cut iscrews for most uses. v

Among the disadvantages of cut-screws I may mention the following :The thread-' cutting is a'time-consuming and expensive operation, it being necessary in the case of relatively small screws to cause the cuttin tool to pass over the work approximate y from six to eight times, and in the caseof relativelv large screws approximately insome cases as i'igh as twenty to twenty-five times, before the roper sizeand shape of thread is formed. his also limits the production of each screw-cutting mechanism to a small number of screws per minute. To facilitate the cutting and reduce the injury to and wear upon the cuttinglltools, it is necessarv to fornr the screw-blah of a hard brittle metal which cuts freely. On the other hand, the use of such hard metal adds to thedifliculties of swaging the heads on the blanks and causes more wear upon the swagmg tools than a softer metal. Furthermore, as the swaging of the head further liar-dens the metal of which the head is formed, this additional liar.-

dening in the case of an originally hard metal blank produces excessive hardness and brittleness, rendering the head liable to s lit and break (particularly through the slot in the operation of cuttin the thread and also in subsequent use, it eing understood that in the thread-cutting operation the blank is turned against the point of a relativel fixed cutting-tool by the engagement with t e slot of a part of the mechanism resembling the point of a screw-driver. As is well known, in the case of cylindrical blanks of metal, such as those from which screws are made, the central unworked and unforged portion of the metal is of inferior strength compared with the exterior or surface portion which has necessarily been worked or forged in the operation of forming the rod or wire from which the blanks are cut. In the formation of cutscrews it is this stronger surface portion of the metal which is principall removed and wasted, leaving the threads ormed by cuts across the fiber of the metal, said fiber extending longitudinally of the blank.

Among the disadvantages of rolled screws I may mention the following: In the heretofore pro osed methods of forming the threads on suc 1 screws (the object being to effect this atone operation) a blank cut to'proper length is introduced cold (Le, not heatet to soften) between two dies relatively movable in a longitudinal direction but which are ri idly held with the workingfaces a fixed istance apartj Said workingfaces have heretofore been providedwith a series of oblique or diagonall extending ribs with intervening grooves, t e face of each rib gradually widening from its front end toward its rear or finishin end while the intervening grooves gradual y widen and become shallower in the reverse direction. At the finishing end of the dies the grooves correspond in depth and shape in cross-section to t e height and shape in cross-section of the screw-t read to be formed thereby onthe screw-blank. As the result of this configuration of the grooves and ribs of the dies, and

.of pressure a plied thereby upon the shank also often injures the dies.

For the formation of an ap roximately perfeet or satisfactory screw-t read it is necessary that the rib or thread shall exactly and completely fill the grooves at the finishing ends of the opposing dies. As alread stated,

while the dies are relatively movab e longitudinally of each other, they are rigidly maintained at a constant distance apart; in fact these dies are commonly made to bear and slide upon each other at one side of the thread-forming portions of their surfaces. The wire stock of commerce from which wood-screw blanks are commonly cut varies slightly in size at different portions of its length and in different rolls of wire, resulting in corresponding variations in the diametrical dimensions of different blanks. The cost of wire stock of exactly uniform size would be prohibitive in wood-screw manfacture. But the greatest variation in the size of blanks probably results in the opera-. tion of heading preceding the rolling of the thread. In this operation the straight metal blank is held at one end in an opening (formed partly in each of two die jaws) closed at one end and counter-sunk or flared at its other end corresponding to the shape of screw-head to be formed. Blows upon the projecting end of the blank upset the same and form a headconforming to the flaring die opening. As is well known, this die-opening rapidly wears, and to constantly renew the dies would be prohibitivelyexpensive. It follows that the blows which form the head also shape the shank of the blank to the worn and enlarged shape of the die-opening. These unavoidable variations in the sizes of blanks result in imperfections in and freuently total destruction of, the screwt iread raised by the (lies, also frequent injury to the dies. If the blank .varies in excess of the required dimensions the displaced metal will fill the grooves before their shallow or finishing ends are reached, resulting in excessive compression causing the blank to slide between the die-faces and injuring or destroying the screw-thread. This sliding of the blank frequently clogs the dies with consequent delays in o eration, and

f the dimensions of the blank are less than required (variations of one or two thousandths of an inch are detrimental) the metal raised in the thread fails to completely fill the die-grooves 5 at their finishing ends. The screw-threads formed under these conditions have rough and uneven peripheral edges. But rolled screws of commerce possess some points of advantage over the well-known cut-screws;

for example, in rolling, blanks of softer metal are used and the swaging of the head does not weaken the 'latter by imparting excessive hardness. The rolling of the thread consolidates, toughens and hence strengthens 6 the normally weaker interior portion of the metal at the same time maintaining an unbroken relation between the thread and the body of the screw and also retains the strong surface portion-of the blank with the fiber of j the metal continued through all the undulations of the threaded surface. on the contrary,in cut-screws this stronger surface portion is mostly cut away and the screw weakened by having the threads formed on the under portion of inferior metal. lolledscrews can be more rapidly and cheaply made thancut-screws. ()n the other hand, the more perfectly formed threads, not exceeding the diameter of the smoothshank portion adjoining the head, gives to cut-screws an advantage which makes them' preferable for most uses over the rolled screws of commerce, in which latter the threads are more or less imperfect and exceed in diameter the smooth shank portion adjoining the head, said 5 smooth portion consequently loosely fitting the opening through which the larger thread portion has entered.

It is my particular object to provide a wood-screw possessing especially those desiro able characteristics of cut-screws which at present render the latter superior for most. uses to rolled screws of commerce; it is also my object to embody in such a screw those desirable characteristics of rolled screws which render the latter in some respects suerior to the well-known cut-screws, and to urther provide a wood-screw possessing points of Sn eriority not present in either the cut or rolle( screws of comm'erce.

It is my further object to improve upon methods heretofore known of forming screwthreads upon articles of commerce such as screws, bolts and the like, whereby this work may be done not only much cheaper (the time, labor and wear upon tools and machinery being minimized), but better than by the known cutting methods.

With these and other objects in view my invention is an improved rocess of manufacturing wood-screws an analogous articles, and particularly of forming the screwthreads thereon.

In accordance with my invention as pref- I erably followed in making wood-screws, I first roll the groove between the threads and subsequently impart the desired form and finish to the thread. Preferably the step of giving the thread its final form is done by cutting, though this may be done by grinding, by a second rolling operation, or otherwise. I refer however to do this by cutting and thus obtain at least to a maximum degree, all of the advantages of both methods as heretofore practiced while eliminating or minimizing their disadvantages.

The rolled thread is made sufliciently large to permit removal. of all irregularities and. proper shaping of the thread by the cutting. Consequently as the shape of the die-grooves 1.30

is not relied upon to impart finished shape to the screw-thread it is not necessary that the raised threads shall at any time in the rolling operation exactly and completely fill the grooves in order to get a properly finished thread. On the contrary, in the'improved dies preferably employed the rooves are made of such depth. as not to be led by the threads at any time durin the rolling operation, whereby I avoid di 'culties above exlained with reference to screw-thread roll- 1ng methods heretofore proposed. While .it is believed that the most satisfactory and economical results may be obtained by first rolling the thread, I may also-especially in the formation of threads on articles other than wood-screws, such as bolts, where saving of expense and rapidity of production are not so essential-do that art of the work by cold forging methods suc as cold-swaging. In those other methods of cold forging it is also essential to the obtainment of the best and satisfactory results,'that the grooves of thefdie members shall be of such depth as not to be filled by the thread.

The above and other important features will be more fully explained in connection with the accompanying drawings, showing the invention a plied to a wood-screw, although as will be readily appreciated, the improvements are also applicable to other articles having a screw-thread or threads thereon.

Figures 1 to 5 illustrate a series of wellknown steps or operations upon screw-blanks preparatory to forming a screw-thread thereon Fig. 1 showing a blank as cut from wire orotherstock, Fig. 2 the blank of Fig. 1 having a head swaged thereon, Fig. 3 the same blank with the head shaved or trimmed, Fig. 4 the same with the head slotted, and Fig. 5 the same pointed and with the head again trimmed to remove burs or rough edges formed in slotting. Fig. .6 shows the blank of Fig. 5 having a screw-thread rolledthereon in accordance with the present invention. Fig. 7 illustrates the screw of Fig. 6with the )eripheral edge of the thread cut or shaved off to remove any roughness, irregularities and unevenness, and to reduce thethread to the desired diameter. Fig. 8 shows the screw of Fig. 7 with the thread sharpened by cutting or trimming its edges. Fig. 9 illustrates one form of cut by which the thread of Fig.- 7 may be sharpened to the shape shown in Fig. 10. other form of cut by which the thread of Fig. 7 may be sharpened to the shape shown in Fig. 12. Fig. 13 is a plan view of one of the improved dies used in rolling the screwthread. Fig. 14 is a section on line 14 of Fig. 13, and Fig. 15 is a transverse section through two dies and a screw in the operation of rolling a thread upon the latter.

In the manufacture of wood-screws, I preflthe grooves.

Fig. 11 illustrates an-this trimmed to present a smooth surface, as

shown in Fig. 3, the slot 22 then cut as shown in Fig. 4, and the head again trimmed to remove burs or rough edges formed in cutting the slot. Point 23 is next formed 'on the blank, asshown in Fig. 5. Although I prefer to carry out these steps in advance of the operation of rolling the' screw-thread, which operation is about to be explained, the order 0 the steps may be changed as found most convenient; for example, the steps of forming, trimming and slotting the head may follow the rolling of the thread. Upon the blank in any suitable form and While cold ('i.e., not heated to soften), I next roll a thread such as shown in Fig. 6. In rolling this thread the best results may be obtained by employing my improved dies 30, 30, such as shown in Figs. 13, 1.4 and 15. These dies, which are preferably exact du .licates, resemble in some respects dies hereto ore used in rolling screwthreads. They have a series of oblique substantially parallel grooves 31, each gradually narrowing from the -end at which the blank enters (left-hand end, Fig. 13) to the end at which said blank leaves the bite of the dies (right-hand end, Fig. 13). These grooves are separated by ribs 32 gradually tapering in a direction oppositethat of the'taper of An important difference 'over dies heretofore known 'for'such work is that are throughout their length of such depth as not to be filled at any point by the screwthread raised on the screw by the rolling operation, not even at the ends of the dies (right-hand end, Fig. 13) which last act on the screw-thread and when the blank is over size. Thus in Fig. 15, intended to show the relative position of two dies at or near the finish of their operation upon a screw, it will be noticed that the grooves are somewhat deeper than the thread on the screw. From peculiarity important results are obtaine slight variations in the. size of blanks do not produce detrimental or injurious results upon the threadsor u on the dies, as previously explained with re erence to rolling methods heretofore practiced. Furthermore, I avoid excessive compression of the threads resulting in objectionable hardness, brittleness and s litting of the metal of which they are formed this being a difficulty frequently encountered where the thread must completely fill the grooves. The formation of the thread by rolling does however. result in toughenin densifying and hardening the metal of t e threaded portion of the screw, and this, articularl in the case where the original bl ank is o relatively soft metal, facilitates any subsequent cutting or trimming of the threaded ortion.

. Another important eature of the dies is the transverse notches across the edges of ribs 31, as shown in Figs. 13 and 14, thus providingteeth which at the start and during a portion of the rolling operation engage the screw-blank to insure rotation of,the blank on its axis during the relative longitudinal movement of the dies. Damage to the screw and dies resulting from sliding of the blank, 'i.e., its failure to rotate on its axis while the dies are in movement,is thus avoided. These notches do not extend to the end of the die which last acts upon the screw, the edges of the ribs at this portion being smooth, so that as the screw leaves the dies the bottom of the groove of the. thread is smooth.

' As is usual, the relative positions of the dies 30, 30 is determined by sliding contact between flat portions 33 of the die block faces. Instead of die-blocks such as shown, I may if preferred, employ rotary disks or rollers having suitable curveddie-surfaces preferably embodying the important characteristics of this invention.

On some ty es of screw-threaded articles, particularly t ose for en agement with an already formed interior y screw-threaded opening, the thread may in some instances be used as formed b the rolling dies without further finishing. ut when a thread of uniform and regular diameter and having a smooth regular peripheral edge is desired, as isusual in the case of wood-screws, I cut or trim oil the peri heral edge of the rolled thread of Fig. 6, re ucing it to the form and diameter'shownin Fig. 7. This operation may be rapidly accomplished.

/ When ,in addition to the characteristics last mentioned, a thread of less thickness, or more tapered, or having a sharpened edge is desired, as is also usually the case in woodscrews, the rolled screw-thread of Fig. 7 having its peripheral'edge cut, is further cut to any desirable shape (such as shown in Figs. 10 and 12) having a sharpened edge. To cut the thread .to the shape shown in Fig. 10, I employ a tool having aocutting-edge of the shape shown in dotted lines, Fig. 9, which-in passing from end to end of the screw (one cutting is usually sufficient) cuts metal from both sides of the thread'withoutremoving any metal from the bottom of the roove beemploy a tool having a cuttiIig-edge of the shape shown in dotted lines, ig. 11, which trims the sides of the thread and preferably the bottom of the cove. With the object of still further minimizing the cuttin where a sharpened thread, such as shown in igs. 10 and 12 is desired, I may omit the first cutting operation for shaving off the peripheral edge of the rolled thread, and rely upon one cutting operation to reduce the rolled'thread (Fig. 6) to its sharpened form.

My improved process, as s ecially desi ned for the manufacture of woo -screws, embodies as its principal feature the formation of the screw-thread by rolling (preferably in dies having rooves of such depth as not to be filled by tie thread) followed by a finishing, shaping o1 sizing of the thread by cutting.

These steps in conjunction with the usual more dense than in its ori inal form, and con-' sequently harder than t e unthreaded ortion of the shank of the finished screw. onsequently, even though aportion of the rolled thread be cut away in finishing or shaping, the final thread is left formed in metal which has been hardened and densified b the rolling and which is harder and more ense than the metal at the unthreaded portion. This increase in density and hardness of the threaded portion renders it practically as strong as the unthreaded portion and the screw of approximatelv uniform strength from head to point. hese characteristics are not present in the heretofore known cutscrew for the reason that in the latter the metal of the 'thread and the unthreaded portion, of the blank are of their original density and hardness, the threaded ortion being further weakened by removal and cutting across the fiber of the stron er surface .metal; it results that the threade portion is much weaker than the unthreaded part. Further more, as compared with the heretofore known rolled-screw the thread of my improved screw exhibits spiral or volute lines made by the action of the cutting-tool or tools in shaping, sizing or finishing the thread, whereas no such lines appear on the thread of the or dinary rolled screw. In those cases in which the entire surface of my rolled thread is not cut the lines of cut a pear onlyon the cut ortio For examp e, if the thread be use in the form shown in Fig. 7, the lines of cut will appear only at the eriphery of the thread; if used in the orm shown in Fig. 10, the lines of cut will appear only on the sides of the thread and not at the bottom of the groove. When my thread has these last mentioned characteristics it is furtherdistinguishable from cut-screws in which the lines of cut cover the entire surface of the threaded-portion, and from rolled screws in which no lines of cut a pear on the threaded portion.

Artie es other than wood-screws, havin threads formed thereon by m combine rolling and cutting operation, wil also exhibit or disclose the distinguishing characteristics above ex lained, or some of them. -My invention a so embraces the im roved method of rolling a thread in which t e latter at no time fills the die-grooves, whether followed by a cutting of the thread or not. Furthermore, I do not limit myself to one or more cutting operations to finish the thread, though as before explained, it is desirable to minimize the same.

While reference has been particularly made to the formation of a single thread (as is customary in most wood-screws) it is to be understood that the invention is'equally applicable to' the simultaneous formation of two or more parallel threads.

I am aware that prior to my invention it has been proposed (as for example, in U. S. Patent No. 54,687, dated May 15, 1866) to forge screw-threads on bolts while hot by feeding the hot blank between cooperating hammer and anvil dies, and for some purposes to ass the bolt thus formed when cold through ishing-dies, it being said to be only necessary to takeoff a very small cut to ive the bolt a fine bearing surface. a materially different method from mine wherein the thread is first formed by cold.

for ing. a

\Il'hat I claim is 1'- 1. In the manufacture of screws and analogous screw-threaded articles, the process of forming the screw-thread consisting in'coldforging the thread on the article, and then bringing said forged thread to the desired dimensions by cutting.

2. In the manufacture of screws and analogous screw-threaded articles, the process of forming the screw-thread consisting in coldrollin a thread on the article, and then brin ing said cold-rolled thread to the de sire dimensions by cuttin 3. Inthe manufacture 0% screws and analogous screw-threaded articles, the process of forming the screw-thread consisting in coldrollin a thread on the article, and then brin ing said cold-rolled thread to the desire diameter by cutting.

4. In the manufacture of screws and analogous screw-threaded articles, the process of forming the screw-thread consisting in forgthan the ori inal diameter of the But this is .ing on the article a thread of larger diameter than the original diameter of the art of the article on which it is forged, and t en bring ing. the thread to the desired dimensions by cutting.

5. In the manufacture of screws and analogous screw-threaded articles, the process of forming the screw-thread consisting in rolling on the article a'thread of larger diameter art of the article on w ich it is rolled, and t en bringing the thread to the desired dimensions by cutting. A

6. In the manufacture of screws and analogous screw-threaded articles, the process of forming the screw-thread consisting in coldrolling on the article a thread of larger diameter than the original diameter of the part of the article on which it is rolled, and then brin ing the thread to the desired dimensions y cuttin 7. The process 0% forming a screw-thread on screws and analogous articles, consisting in cold-forgin a thread without limiting expansion of t e thread in a radial direction in the forging operation.

8. The process of forming a, screw-thread on screws and analogous article's, consisting in radially indenting the article to form the groove separating convolutions of the thread, and throughout said indentin o eration leavin that ortion of the articIe aibng the line 0 the tiread free to unlimited radial expansion.

9. The process of forming a screw-thread on screws and analogous articles, consisting in radially indenting the article to form the groove separating convolutions of the thread, and throughout said indentin o eration leaving that portion of the article a ong the line of the thread free to unlimited radial exansion, and then cutting'the thread thus ormedxto finish the same.

' 10. The process of forming a screw-thread on screws and analo ous articles, consisting in indenting the artic e by rolling to form the groove separating convolutions of the thread and throughout this operation leaving that portion of the article alon thread free to unlimited ra ial expansion.

, 11. The process of forming a screw-thread on screws and analo ous articles, consisting in indenting the artic e by rolling to form the groove separating convolutions of the thread and throughout this operation leaving that portion of the article along the line of the thread free to unlimited radial expansion, and then cutting the thread thus formed to the desired dimensions.

12 The process of manufacturiri screws, consisting in forgin a head and co d-rolling a thread ona suitab e blank, and then bringing the thread to the desired dimensions by cutting.

the line of the w 13. In the manufacture of screws and anal- 0 ous screw-threaded articles, the process w ch consists in coldforging a screw-thread on the article, and then removing r'naterial 5 from said forged thread to bring it to the desired dimensions.

In testimony whereof I have signed this specification in the presence of two subscribmg Witnesses.

WILLIAM G. ALLEN.

Witnesses:

FREDERICK A. HoL'roN, W. B. KERKAM. 

